There are numerous medical conditions when it is desired or necessary to close a body vessel, including for instance in the treatment of aneurysms, arteriovenous malformations, arteriovenous fistulas, for starving organs of oxygen and nutrients for instance in the treatment or containment of cancerous growths, and so on.
Several techniques are known and in use for closing or occluding such body vessels. Traditionally, vessels have been closed by means of external ligation, which generally must be carried out by an open surgery procedure, with its associated risks, inconvenience and long patient recovery times. Other more recent methods aim to use an endoluminal procedure to insert into the vessel or organ one or more occlusion devices, such as a metal framed occluder, pellets or the like, able to obstruct the flow of blood in the vessel.
It is also known to seek to constrict a vessel by endoluminal ablation, causing contraction of the vessel and/or coagulation of blood to form a blood clot in the vessel. A technique which has been considered suitable is RF ablation, in which an electrical terminal is fed endoluminally into the vessel and an electrical pulse at RF frequencies applied to the electrical terminal. The conductivity of blood and/or the vessel tissues causes localised heating. This heating can be used to cause damage to the tissue (intima) of the vessel wall, resulting in vessel contraction. In other devices RF ablation heats the surrounding blood, causing this to coagulate around the electrical terminal and form a blood clot which blocks the vessel.
Two types of RF ablation apparatus are generally contemplated in the art, the first being a monopolar system having an elongate anode terminal and a cathode pad. The anode terminal is designed to be fed endoluminally into the patient's vessel, while the cathode pad is positioned against the person's outer body, as close as practicable to the anode terminal. Electrical energy applied to the anode terminal will pass by conduction through the patient to the cathode pad. There will be localised heating at the anode terminal, which effects the desired ablation.
A problem with monopolar systems is that it can be difficult to control the extent of damage to surrounding tissues and organs, as well as to the vessel wall. This risks damaging the vessel to the point of rupture, as well as possible irreversible damage to neighbouring organs.
Another RF ablation system uses a bipolar arrangement, in which an elongate electrical element includes both the anode and cathode terminals, which are spaced longitudinally from one another at a distal end of the electrical element. Current passes between the anode and the cathode terminals through the surrounding blood, causing localised heating and coagulation of the blood. A bipolar system has been considered to provide more localised heating and therefore reduced risk of damage to surrounding organs and tissue.
A problem particularly with a bipolar system, but also experienced in a monopolar system, lies with the retraction of the electrical terminal from the vessel at the end of the ablation process. In a system which ablates the vessel wall to cause its contraction, the electrical terminal can become attached to the vessel wall tissue, with the risk of tearing and rupturing the vessel wall. In a system which ablates the surrounding blood to generate a blood clot in the vessel, there is the risk that the blood clot is dragged with the electrical element and that the occlusion of the vessel is as a consequence lost. There is also the risk of leaving an opening in blood clot where the electrical terminal resided, which can result in incomplete occlusion and the risk of recanalization.
Some such devices have attempted to address the above problems by having an electrical element with a detachable terminal end. However, this entails leaving a foreign body in the patient.
Examples of prior art devices and methods can, for instance, be found in US-2009/0248007, US-2001/0020167, US-2001/0016739, U.S. Pat. No. 6,539,265, WO-2010/080974, U.S. Pat. Nos. 6,264,650, 6,066,139, 6,676,657, US-2010/0268217, U.S. Pat. Nos. 5,709,224, 6,398,779 6,019,757 and 5,743,905.